With rising epidemic obesity in US women of childbearing age, obesity is an increasing threat to healthy development of the fetus. Obesity adversely impacts maternal and child health-and ultimately the health of our communities and nation. Gestational diabetes (GDM) during pregnancy is rising in parallel with population obesity, and there is likely a large proportion of women with GDM who can now be recognized in the 1st trimester of pregnancy (early GDM)-but this is essentially unstudied. We propose to initiate a new clinical care protocol to screen all high-risk obese pregnant women for early GDM at their first prenatal visit in the Northwest and Hawaii regions of Kaiser Permanente, where universal GDM screening is now routine at 24-28 weeks gestation (usual GDM). We hypothesize that early GDM represents a more aggressive phenotype, and because of associated obesity, may account for a large proportion of current GDM- associated adverse outcomes. Among a high-risk multi-ethnic population of over 59,000 pregnant women and their babies (118,000 total), we will evaluate maternal and perinatal GDM-associated outcomes as it relates to obesity, and the impact of the universal early GDM screening intervention on these outcomes from the perinatal period to birth. Like an RCT, our intervention is hypothesis driven, but because of its setting-in the clinical care of a large HMO-it can test the entire population, rather than only healthy volunteers who typically participate in an RCT. The long-term objectives are to fill in the critical knowledge gaps in GDM research, particularly as it pertains to population obesity, and to reduce GDM-associated adverse maternal and perinatal outcomes. Our specific aims are to compare early versus usual GDM both in prevalence of diagnosis and compare how these groups differ in outcomes for mother and baby; to determine the impact of measured maternal weight (both initial and gain during pregnancy) as an independent predictor of GDM-associated maternal and perinatal outcomes; and to determine the sensitivity and specificity of screening tests for early GDM. In addition, we will evaluate whether advancing GDM detection to the first trimester in high-risk obese women will improve maternal and perinatal outcomes at the system-level. The study population will be the entire at-risk population of pregnant women in two Kaiser regions, representing a multi-ethnic and socio-economically diverse cohort. PUBLIC HEALTH RELEVANCE: PROJECT NARRATIVE This project will screen for early diabetes in pregnancy in all obese pregnant women at their first prenatal visit, among a study population of over 59,000 pregnant women and their babies (118,000 total) in a large diverse HMO, to determine if early gestational diabetes diagnosis and treatment of high- risk women reduces complications for the baby and the mother.